Branched polysiloxanes



United States Patent 3,361,714 BRANCHED POLYSILOXANES George M.Omietanski, Tonawanda, N.Y., assignor to gnilin Carbide Corporation, acorporation of New or No Drawing. Filed Apr. 29, 1%3, Ser. No. 276,17021 Claims. (Cl. 260-465) This invention relates to branchedpolysiloxanes of specific desired compositions and to a process fortheir preparation employing a tertiary amine catalyst. Moreparticularly, it relates to the production of branched polysiloxaneshaving superior low temperature properties in addition to havingdesirable high temperature properties.

Organopolysiloxane oils and elastomers are known to possess desirablehigh temperature properties. Their use at relatively low temperatureshas been limited, however, by their relatively high freezing points orcrystallization temperatures and high viscosities at low temperatures.Attempts have been made in the prior art to improve the low temperatureproperties of organopolysiloxane fluids and elastomers by introducingbulky groups or branches to the regular structure of theorganopolysiloxane. This introduction of new groups is generallyaccomplished by copolymerization of monomer mixtures or equilibrationtechniques. The resulting branched organosiloxanes prepared byequilibration contain both long and short chains as well as cyclicnetwork components in a random distribution. While these compounds havesome improvement in the general low temperature properties, they stillleave much to be desired in regard to such properties.

I have now found that branched polysiloxanes of specific desiredcomposition having non-random, ordered structure can be prepared, whichhave superior low temperature properties, such as lower pour points orfreezing points and lower viscosities than linear siloxanes of the sameweight average molecular weight. Such materials also have hightemperature properties which are equal to or better than those of linearorganosiloxanes of the same bulk viscosity. These novel branched chainorganosiloxanes have the generic formula:

wherein R and R are monovalent hydrocarbyl radicals, R is a monovalenthydrocarbyl radical or substituted monovalent hydrocarbyl radical, n isa number having a value of 0 to 25 inclusive, m is a number having avalue of 1 to 21 inclusive, w is a number having a value greater than 0,Z is a monovalent radial selected from hydrogen and R3Sl-gIOUPS, and Zis a monovalent radical selected from the class consisting of hydroxyland R SiO groups. Especially useful polymers are obtained when n has avalue of 0 to inclusive, m has a value of 1 to 9 inclusive and w has avalue of l to 500 inclusive. Preferred polymers are obtained when n. hasa value of 1 to 6 inclusive, m has a value of l to 6 inclusive and w hasa value of 1 to 6 inclusive.

When w is l and n and m are equal, the polymer product will have threesubstantially equal length branches attached to a central silicon atomthrough Si-O- Si linkages. The central silicon atom will also have amonovalent hydrocarbyl radical attached to it through a silicon-carbonlinkage. When w is l and n and m are unequal, the polymer product willhave three branches attached to a central silicon atom through Si-O-Silinkages, two of which branches will be of substantially equal lengthand the third branch will be of different length. Here again, thecentral silicon atom will also have a monovalent hydrocarbyl radicalattached to it through a "ice silicon-carbon linkage. The abovedescribed polymer structures are referred to herein as Star polymers.When w is greater than 1, the polymer product will consist of a linearorganosiloxane chain having multiple (R SiO) SiR branches attachedthereto through Si-O-Si linkages and where such branches are uniformlyspaced along the organosilo-xane chain at intervals measured by (R SiO)groups. Such polymer structures are referred to herein as Comb"polymers.

The monovalent hydrocarbyl radicals which are represented by R, R and Rin the above formula are illustrated by alkyl groups, such as methyl,ethyl, propyl, isopropyl, butyl, isobutyl, amyl, hexyl and the like;alkenyl groups, such as vinyl, allyl and the like; alicyclic groups,such as cyclopentyl, cyclohexyl and the like; aryl groups, such asphenyl, naphthyl and the like; aralkyl groups, such as benzyl,phenylethyl and the like; and alkaryl groups, such as tolyl,ethylphenyl, xylyl, mesityl and the like. R, R and R can be the same ordifferent radicals and R, R and R are preferably methyl radicals. Thesubstituted monovalent hydrocarbyl radicals which are represented by Rin the above formula contain chloro, amino or cyano substituents locatedat least two carbon atoms from the silicon atom. Such radicals areillustrated by gamma-chloropropyl, beta-aminopropyl, delta-cyanobutyland the like.

The branched chain polysiloxanes of the present invention havingsuperior low temperature properties can be preferably obtained by anovel process. This preparation process comprises reacting anacyloxy-siloxane having the formula:

R SiO (R SiO)m$ i(OZ)2 with a hydroxy-containing siloxane selected fromthe class consisting of organosiloxane diols having the formula HO(RSiO) H and organosiloxanols having the formula R Sio(R SiO),,H in thepresence of a tertiary amine, wherein R, R R m and n are defined aboveand Z is an acyl radical. The acyl radicals that are represented by Z inthe above formula are illustrated by acetyl, propionyl, butyryl, benzoyland the like, Z is preferably acetyl.

Tertiary amines useful in this preparation process are illustrated bytriethylamine, trimethylamine, triphenylamine, methyldiethylamine,pyridine, methylethylphenylamine, 3-picoline and the like. Tertiaryamines are the preferred catalysts for this preparation reaction sincethey do not react with acyloXy-siloxanes as do ammonia, primary andsecondary amines. Tertiary amines prevent undesirable side reactions andallow specific desired products to be obtained. Ammonia can be used, ifdesired, in the later stages of the reaction to drive it to completion.The tertiary amines are employed in amounts in excess of that requiredto accept the acid formed in the reaction.

When the hydroxy-containing siloxane employed in the above preparationprocess is an organo-siloxane diol, the product can be ahydroxy-endblocked Comb polymer. Such product can be directly used forthe production of organosiloxane elastomers having superior lowtemperature properties. If a stable organo-siloxane fluid is desired,the above hydroxy-endblocked Comb polymer is reacted with anorganosilane having the formula R SiX in the presence of an aminecatalyst to substitute the hydroxyl end-blocking groups with RSiO-groups. X is selected from the class consisting of chloro and OZradicals wherein Z is defined above. Useful catalysts in their latterendblocking reaction are amines such as ammonia, methylamine,diethylamine, pyridine, triethylamine and the like. When thehydroxy-containing siloxane employed in the above preparation process isan organo-siloxanol, the product is a Star polymer which is generally afiuid.

In the formation of bomb polymers by the above preparation process, themolecular weight of the product is controlled by the relative mole ratioof organosiloxane diol/acyloxy-siloxane. It is preferred to use anexcess of the organosiloxane diol in order to form a hydroxyendblockedproduct. Inert organic solvents, such as acetone, benzene, xylene andtetrahydrofuran, are preferably also used in the above preparationprocess to aid in the formation of the specific desired products. Thepreparation process conditions are not narrowly critical. Anacyloxy-siloxane can be reacted with a hydroxy-containing siloxane inthe temperature range of about 0 C. to about 150 C. The preferredtemperature range is from about C. to about 100 C. The reaction of the RSiX end-blocker with the hydroxy-endblocked comb polymer employs thesame general reaction conditions as described above.

In addition to the production of Comb polymers, the reaction between anacyloxy-siloxane and an organosiloxane diol can produce branched cycliccompounds having the formula R SiO(R SiO) Si(R )O[R SiO] wherein R, R Rand m are defined above and a has a value from 3 to 4 inclusive, such as[Me SiO (Me SiO) SiMeO] (Me SiO) 3 Me designates the methyl CH radical.The production of such branched cyclic compounds is favored by a highdilution if inert solvent, such as those mentioned above. By highdilution is meant having the inert solvent present in an amount fromabout 25 to about volume percent based on total volume of reactionmixture (includes solvent, reactants and catalyst).

The reactants in the above preparation process are prepared bywell-known procedures. The HO(R SiO) I-I compounds are prepared byhydrolysis of corresponding acyloxy-endblocked diorganosiloxanes. The

compounds are conveniently prepared by reaction between R SiO(R SiO Hand R Si(OZ) The R SiO (R SiO) H compounds are conveniently prepared byhydrolysis of R SiO(R SiO) (OZ') in the presence of an acid acceptorsuch as ammonium hydroxide, R, R R Z, in and n are defined above.

The branched chain olysiloxanes of the present invenr tion, preferablythe Comb polymers, can be compounded as a gum with fillers and curingcatalysts employing conventional methods and then heat cured underpressure by conventional means to form elastomers having superior lowtemperature properties. In producing the siloxane elastomers, I canemploy as curing catalysts organic peroxides such as the alkylperoxides.Especially suitable curing agents are the dialkyl peroxides which can begraphically depicted by the formulas tit wherein R represents the samealkyl group throughout or alkyl groups of two or more difierent typesand n is zero or a larger integer. Among the specific curing agents thatI prefer to employ when the gum contains olefinically unsaturatedhydrocarbon groups are included:

Di-tertiary-butyl peroxide; Tertiary-butyl-triethylmethyl peroxide;Tertiary-butyl-tertiary-triptyl peroxide, the composition of which isrepresented by the structural formula:

and dicumyl peroxide. Where the organosiloxane gum contains noolefinically unsaturated hydrocarbon groups it is preferred to employorganic peroxides such as dibenzoyl peroxide, 2,4-dichlorobenzoyiperoxide, tertiarybutyl perbenzoate and the like. The amount of thecuring catalyst employed in producing the siloxane elastomers of thisinvention can be from 0.5 part catalyst per 100 parts of the siloxanegums to 5.0 parts catalyst per 100 parts gum. It is preferred to employfrom 1.0 to 2.0 parts catalyst per 100 parts of the siloxane gum inorder to obtain fully cured elastomers.

Among the fillers which may be employed in the production of theelastomers of this invention are inorganic fillers; for example,lithopone, ferric oxide, titanium dioxide, finely divided silica and thelike; and various forms of carbon such as finely divided and colloidalcarbon; for example, carbon black, such as, channel black, gas black,furnace carbon, acetylene black, and the like. The fillers may beincorporated in the elastomer in amounts ranging from 10 to parts byweight filler per parts by weight of the orgauopovlysiloxane gum. It ispreferred to employ the filler in amounts of from 25 to 50 parts byWeight filler per 100 parts by weight of the organopolysiloxane gum.

The invention is described in further detail in the following examples.

PREFARATION OF STARTING MATERIALS HO(R SiO) H and Me designates methylradical, having values of n' up to 9 were isolated in pure form. Thispreparation was repeated and several of the product fractions werefurther identified as indicated below. In these compounds the Ac radicalWas an acetyl radical.

Compound B.P.lmin. Hg Percent AcO Percent AcO Galod Found AoO (MeSiOhAe. 106407/10 36. s 36. 2 AcO (MerSiO); as 73/0. 15 29. 6 30.0AeO(Me1SiO)5Ac 100/0. 2 25.0 25. 2 A00 (MegSiOhAG 137/1. 1 21. 6 21. 3

Higher molecular weight AcO(Me SiO) Ac fluids can be prepared by usinglesser amounts of acetic anhydride.

Hydroxy-endblocked polydimethylsiloxanes were prepared by hydrolysis ofthe corresponding acyloxy-endblocked polydimethylsiloxanes. In general,the acyloxyendblocked siloxane was dissolved in either acetone ortetrahydrofuran to form about a 0.25 molar solution. This solution wasthen treated until hydrolysis was complete with an excess of water(l501000% over theoretical) or with ammonium hydroxide (until themixture remained basic) at 25 C. or below. Complete hydrolysis wasobtained in less than minutes with ammonium hydroxide. After hydrolysiswas complete, the siloxane layer was washed to neutrality and dried overanhydrous calcium sulfate. The resultingalpha-omega-polydimethylsiloxane-diols were then isolated in pure formby distillation. Several of the product fractions were furtheridentified as indicated below.

Into a 5-liter, 3-necked flask equipped with a stirrer, thermometer andreflux condenser, were placed trimethylacetoxysilane (557 g., 4.22moles), dimethylsiloxane cyclic trimer (1875 g., 8.43 moles), and zincchloride (24.3 g., 1 weight percent). The reactants were heated in aconstant temperature oil bath at 115 C. for 46.5 hours with vigorousstirring. The reaction mixture was then cooled, filtered and thefiltrate fractionated. There was thus obtained a 41 mole percent yield(based on total moles of reactants) of Me SiO(Me SiO) Ac having B.P.106108/10 mm. Hg. Analysis indicated 16.6% AcO; theory=16.6% AcO. Alsoobtained was a 23 mole percent yield of Me SiO(Me SiO) Ac having B.P.95100/ 0.15 mm. Hg. Analysis indicated 10.5% AcO; theory=l0.2% AcO.

R SiO(R SiO) H Hydrolysis of Me SiO(Me SiO) Ac was carried out inacetone solution (about 0.25 molar) with an excess of water (about 100%)at 0-25 C. in the presence of an acid acceptor such as ammoniumhydroxide. Hydrolysis was complete in less than an hour. The product wasisolated by flooding the reaction mixture with water and extracting withbenzene. The benzene solution was dried over anhydrous calcium sulfate,freed from benzene and fractionated. The product, Me SiO(Me SiO) H, wasobtained in better than 90 mole percent yield and had a boil ing pointof 70 C./2.5 mm. Hg. Analysis indicated 5.2% OH; theory=5.44% OH.

Me SiO (Me SiO) H was obtained in a similar manner. This product wasobtained in 83 mole percent yield and had a boiling point of 140-142/ 4mm. Hg. Analysis indicated 3.0% OH; theory=3.1% OH.

was pre- Me SiO Me SiO H with excess MeSi(OAc) The product had a boilingpoint of 138 C./0.23 mm. Hg. Analysis indicated 15.0% AcO; theory=17.0%AcO.

Example 1 Into a 500 ml., 3-necked flask equipped with a stirrer,thermometer, gas inlet tube, and addition funnel was charged 104.4 g. ofHO(Me SiO) H and 110.0 g. of Me SiO(Me SiO) SiMe(OAc) The charge wasweighed on an analytical balance and was rinsed into the flask with aminimum amount of benzene. Triethylamine (23.8 g.) was then added slowlyto the charge over a 5 minute period. Under good agitation, the reactiontemperature increased from 24 C. to 51 C. Agitation was continued untilthe reaction temperature decreased to 25 C. (1.5 hours). Anhydrousammonia was then bubbled into the reaction mixture for about 3 hoursuntil no further reaction was observed. During the initial phase of theammonia reaction, the reaction temperature became about 70 C. and acooling bath was applied. Excess MCgSlOAC (30.0 g.) was then added tothe reaction mixture using anhydrous ammonia as the catalyst. Thereaction temperature increased from 25 C. to 43 C. and ammonia waspassed through the reaction mixture until the reaction contents reached25 C. (3 hours). The reaction mixture was then quenched into an excessof water, the siloxane layer was Washed to neutrality, dried overanhydrous calcium sulfate and devolatilized with a nitrogen sparge to200 C. The product was cooled and filtered. The yield was about 60 molepercent of a Comb polymer having the formula:

The low boiling reaction obtained in the devolatilization of the abovecompound was fractionated to yield a branched cyclic compound,

having the properties of B1. 113-115 C./1.0 mm., Hg, n =l.3984; d=0.9578. Calculated for C H O Si =molecular weight=592; molar refraction(MR =149.1 Found: molecular weight=599, MR =149.3.

Example 11 Into a 500 ml., 3-necked flask equipped with a stirrer,thermometer, gas inlet tube and addition funnel were charged 110.0 g. ofMe SiO(Me SiO) SiMe(OAc) and 48 g. of triethylamine. To the additionfunnel was charged 104.4 g. of HO(Me SiO) H and approximately half of itwas added to the flask during the course of an hour. A cooling bath wasapplied and the remainder of the diol was added while dry ammonia waspassed through the reaction mixture (1.5 hours). After the addition ofthe diol was completed, ammonia was passed through the reaction mixturefor an additional 3 hours. Then, Me SiCl (22.0 g.) was slowly addedusing ammonia as a catalyst (2 hours). The reaction mixture was thenquenched into excess water, the siloxane layer was washed to neutrality,dried over anhydrous calcium sulfate and devolatized with a nitrogensparge to 200 C./ 5 mm. Hg. The product was cooled and filtered. Theyield was about 62 mole percent of a compound having the formula;

Preparations of Comb polymers similar to those described in Examples Iand 11 above were repeated to form various Comb polymers. These branchedchain polymers and some of their characteristics are listed below.

TABLE I.MOLECULAR WEIGHT AND MOLAR REFRAC- TIONS O1 SILICONE COMBPOLYMERS Calculated Structure Mn M Obs. MED MRD Calcd. Caled. Obs

(D:):.24D'*1.m\i 1.079 1,117 289.7 225.1 M(D3)2.53D1 1351 1, 079 1, 293333. 327. s i tDahmDtnw 2, 559 1, 18 397. 1 39 6 0 113 .QGDLQE 2, 5502,130 540. 2 541. s a)4 .eDa 51M 5, 087 2, 353 607. 4 002. 2M(Da)-1.75D5.15I-I 5. 087 2, 007 054. 0 057. 1 1.1 D5 g ..r t.-.1.1 2,32s 2, 000 515. 2 507. 5 M(D5)3.5:D'2.52M 3.017 2,400 611. 8 608.2 t)2,m'1.10 1,079 1,500 384.2 681.6 MtDfimnDt .11 2, 589 2, 072 527. 0 523. 3M (D5)6.02D'' nz1v. 589 4, 700 11114.0 1, 182. 5 Muimmo 11 5,057 5,2001,310. 5 1,307.7 s)2.14 "*1 07 1,557 370. f 394. 5 u1.135D"1.1... 1,0791, 783 451 7 451.2

The calculated molar refractions (MR and the calculated structures arebased on the observed molecular weights. The observed molecular weightswere obtained using the vapor pressure osmometer.

Example 111 Me SiO (Me SiO SiMe (OAc) 2 (70 g.) and HO(Me SiO) I-I (46.5g.) in benzene (469.0 g.). After the addition of the triethylamine wascompleted in about minutes, the reaction mixture was heated andmaintained at 80 C. for about 17 hours. The reaction mixture was thencooled and additional 300 g. of benzene was added, and dry ammonia wasbubbled through the reaction mixture for about 3 hours. The reactionmixture was then filtered and the filtrate stripped of solvent andfractionated. There was obtained about g. (26 mole percent) yield of abranched cyclic pentamer having the formula [Me SiO(Me SiO) SiMeO] (MeSiO) It had the properties of 13.1 140 14? C./2.0 mm. Hg n =l.3987; d=0.9614. Calculated: molecular weight=666, MR 168.7. Found: molecularWeight:665, MR 167.4.

Example IV In a 5110 ml., 3-necked flask equipped with a stirrer,addition funnel and gas inlet tube were placed Me SiO (Me SiO S1Me OAc)2 (116 g., 0.245 mole) and triethylamine ,(80 g., excess). The compoundMe SiO(Me SiO) I-I (160 g., excess) was then slowly added over a periodof 0.5 hour from the addition funnel, followed by the addition of anexcess of ammonia through the gas inlet tube. After cooling, thereaction mixture was quenched into distilled water, the siloxane layerwas separated, dried over anhydrous cal cium sulfate and fractionated.There was obtained 120 g. (50 mole percent yield) of [Me SiO(Me SiO)SiMe having a boiling point 165 /0.2 mm. Hg. Calculated forC28H34O12S1131 C, H, S1, MR1): 254.0, mol. wt. 978. Found: 34.2% C, 8.8%H, 37.0% Si, MR :254.0, mol. wt. 987.

Example V a (M62810) 3] SiC H This star polymer product had theproperties of 13.1.

178 C./0.08 mm. Hg; n =l.4l62. Calculated for (3 11 0 81 38.2% C, 8.3%H, 35.1% Si, MR =273.8,

molecular weight=l038. Found: 38.3% C, 8.2% H, 35.1% Si, MR =274.0',molecular weight l032.

The most important single property of branched siloxane polymers istheir extremely low pour points or freezing points. This propertyappreciably extends the service temperature range of these materials.The pour points were obtained with a modified Beckman freezing pointapparatus. The apparatus provided for liquid nitrogen as the coolant, aconstant purge of argon over the sample, insertion of the thermocoupledirectly in the sample, and vigorous agitation of the sample by means ofa hand operated wire stirrer. Pour points were determined on the fluidsby continuously stirring the samples as they cooled, and takingtemperature versus time readings at 1 minute intervals. In the region ofthe pour point, 30 sec. intervals were employed. The plateau on thetimetemperature plot was taken as the lower limit of the pour point. Atthis temperature the fluid could no longer be stirred. At least twocooling curves were run on each sample together with a melting curvedetermination to eliminate supercooling eitects. The pour points ofnovel branched siloxane fluids and linear siloxane fluids which servedas controls are given in Table 11 below. Generally, the data shows thatthe pour points of the novel branched fluids are about 40- 50 F. lowerthan those of linear dimethylsiloxane fluids of comparable molecularweight or comparable 25 C. bulk viscosity. The best pour points areobtained with the most highly branched dimethylsiloxane fluids of lowmolecular Weight.

TABLE II.1?OUR POINTS OF BRANOHED SILICONE FLUIDS The low temperatureproperties of the novel branched siloxane polymers are also superiorwhen time at temperature is considered. A comb polymer having theformula M(D (MD T) M was still fluid after 18 days at F. but a 20 cstks,linear dimethylsiloxane oil crystallized within 3 days. At 139 F., the20 cstks. linear fluid crystallized within an hour. 1

Blends of novel branched siloxane polymers and linear siloxane fluidsalso show excellent low temperature properties, particularly at higherbranched fluid concentrations. For example, a 10' cstks. lineardimethylsiloxane fluid crystallized within 0.5 hr. at 139 F., but a50/50 weight percent blend of this fluid With a branched chain combpolymer of formula M(D (MD T) M was still fluid after 7 hours at 139 F.

The novel branched siloxanes also have high temperature properties whichare comparable to linear siloxane fluids. Branched fluids in the 2000molecular weight (number average) range had flash points of 465-535 F. Afully stabilized linear dimethylsiloxane fluid has a flash point undersimilar conditions of about 500 F. in this molecular weight range.

The novel branched organopolysiloxanes of the present invention can beused in any manner similar to prior organopolysiloxanes, such aslubricating oils and elastomers for gaskets and the like. In addition tosuch prior art utility, the present novel compositions have superior lowtemperature properties which greatly extends the utility of the fluidsand elastomers prepared therefrom to such low temperatures.

Utility for the branched chain organopolysiloxanes of the presentinvention is shown by the following example.

Example VI The thermal condensation reaction of Me SiO(Me SiO) Si(Me)(OOCCHQ with a stoichiometric equivalent of HO(Me SiO) I-l Where n isabout 76 (0.3 weight percent OH) gave a slightly sticky and crosslinkedcopolymer which contained about 0.6 mole percent of Me Si(Me SiO) SiMeOpendent units. This copolymer was prepared by the following heatingschedule: 200 C./760 mm. Hg for 3 hr.; 180 C./5 mm. Hg for 6 hr.; 180C./1 mm. Hg for 6 hr.; and 250 C./1 mm. Hg for 6 hr. The copolymen'c gumwas compounded in a mixture consisting of 100 parts by weight gum, 40parts by weight finely divided silica filler, 2 parts by weight Fe Ostabilizer, and 2 parts by weight benzoyl peroxide curing catalyst. Thismixture was then placed in a mold and heated to 240 F. for min. The moldcured elastomer product was post cured at 480 F. for 24 hours. Thephysical properties of the elastomer product are listed below. Thereappeared to be no loss of physical properties due to rearrangement ofpendent siloxane groups during post curing.

TABLE III Properties Mold Cure Post Cure Hardness (Shore A) 70 72Elongation (Percent) 150 125 Tensile, p.s.i 530 575 Permanent Set(Percent) O 0 wherein R and R are monovalent hydrocarbyl radicals, R isselected from the class consisting of monovalent hydrocarbyl radicalsand substituted monovalent hydrocarbyl radicals, that contain a chloro,amino or cyano substituent located at least two carbon atoms from thesilicon atom, n. is a number having a value of 0 to 25 inclusive, m is anumber having a value of l to 21 inclusive, w is a number having a valuefrom 1 to 6, Z is a monovalent radical selected from the classconsisting of hydrogen and R Si groups, and Z is a monovalent radicalselected from the class consisting of hydroxyl and R SiO groups, and (2)branched cyclic organosiloxanes having the formula:

R: [(lt siomt simms io:imt sio].

wherein R, R R and m are defined above and a is a number having a valuefrom 3 to 4 inclusive.

2. An organosiloxane as defined in claim 1 which is a liquid.

3. An organosiloxane as defined in claim 1 which is a liquid having aviscosity from 7.0 to 135.3 centistokes at 25 C.

4. Branched chain organosiloxanes with superior low temperatureproperties having the formula:

wherein R and R are monovalent hydrocarbyl radicals, R is selected fromthe class consisting of monovalent hydrocarbyl radicals and substitutedmonovalent hydrocarbyl radicals, that contain a chloro, amino, or cyanosubstituent located at least two carbon atoms from the silicon atom, nis a number having a value of 0 to 25 inclusive, m is a number having avalue of 1 to 21 inclusive, w is a number having a value from 1 to 6, Zis a monovalent radical selected from the class consisting of hydrogenand R Si groups, and Z is a monovalent radical selected from the classconsisting of hydroxyl and R SiO groups.

5. Branched chain organosiloxanes as set forth in claim 4 wherein n hasa value of O to 15 inclusive, in has a value of 1 to 9 inclusive and whas a value of 1 to 500 inclusive.

6. Branched chain organosiloxanes as set forth in claim 4 wherein n hasa value of 1 to 6 inclusive, m has a value of 1 to 6 inclusive and w hasa value of 1 to 6 inclusive.

7. Comb branched chain organosiloxanes as set forth in claim 4 wherein whas a value greater than 1.

8. Star branched chain organosiloxanes as set forth in claim 4 wherein whas a value of 1.

9. An organosiloxane as defined in claim 4 which is a liquid having aviscosity from 7.0 to 135.3 centistokes at 25 C.

10. Branched chain organosiloxane having the formula:

11. Branched chain organosiloxane having the formula:

ie (MezSiO) S iO (MezSiO);SiMe;

O-(NIBgSiOhSiMGgJiA; 12. Branched chain organosiloxane having theformula:

Me (MezSiO) t-s'r (Metsio SiMez o (Metsio SiMe NH .5, 13. Branched chainorganosiloxane having the formula:

Me (MezSiOh-Sb-O (Me SiO) SiMe ez$ )x 8a 1.10-5.64 14. Branched chainorganosiloxane having the formula:

(Me2SiO)qSiO -(MezSi0) SiMe O(MezSiO) aslMea 1.135 15. Branched chainorganosiloxane having the formula:

[Me SiO(Me SiO) SiMe 16. Branched chain organosiloxane having theformula:

[Me SiO (Me SiO) SiC H 17. Branched cyclic organosiloxanes with superiorlow temperature properties having the formula:

MegSiO MGgSiO Measio wherein R and R are monovalent hydrocarbylradicals, R is selected from the class consisting of monovalenthydrocarbyl radicals and substituted monovalent hydrocarbyl radicalsthat contain a chloro, amino, or cyano substituent located at least twocarbon atoms from the silicon atom, m is a number having a value of l to21 in- 19. Branched cyclic organosiloxane having the formula:

[Me SiO (Me SiO) SiMeO] [Me SiO] 3 20, Branched cyclic organosiloxanehaving the formula:

[Me SiO(Me SiO) SiMeO] [Me SiO] 4 21. A heat-curable elastomer formingcomposition comprising (1) a branched chain organosiloxane having theformula:

R2 Z[ Ri si0)ns io -(Rg SiO) SiRz i.1 wherein R and R are monovalenthydrocarbyl radicals, R is selected from the class consisting ofmonovalcnt hydrocarbyl radicals and substituted monovalent hydrocarbylradicals that contain a chloro, amino, or cyano substituent located atleast two carbon atoms from the silicon atom, 12 is a number having avalue of 0 to 25 inclusive, m is a number a value of 1 to 21 inclusive,w is a number having a value greater than 0, B is a monovalent radicalselected from the class consisting of hydrogen and R Si groups, and Z isa monovalent Qradical selected from the class consisting of hydroXyl and.R SiO groups, (2) a filler and (3) an organic peroxide, j

References Cited UNITED STATES PATENTS 3,077,465 2/1963 Bruner 260-44383,105,061 9/1963 Bruner 260-448.8 3,234,175 2/1966 Pike 260-4653,271,360 9/1966 Williams 260-465 DONALD E. CZAJA, Primary Examiner.

LEON I. BERCGVITZ, Examiner.

M. I. MARQUIS, Assistant Examiner.

1. BRANCHES ORGANOSILOXANES WITH SUPERIOR LOW TEMPERATURE PROPERTIESSELECTED FROM THE CLASS CONSISTING OF (1) BRANCHED CHAIN ORGANOSILOXANESHAVING THE FORMULA:
 21. A HEAT-CURABLE ELASTOMER FORMING COMPOSITIONCOMPRISING (1) A BRANCHED CHAIN ORGANOSILOXANE HAVING THE FORMULA: